System and method for insertion of flexible spinal stabilization element

ABSTRACT

Insertion of a spinal stabilization element into a patient generally includes positioning a cord within a sheath and inserting the sheath and cord through the patient&#39;s body along a path generally toward an anchor member. An advancement member may be mounted on the leading end of the cord to further facilitate this insertion. The sheath is then retracted to expose a first portion of the cord within the patient&#39;s body, and the first portion of the cord is moved into a desired position relative to the anchor member. After advancing a spacer over the sheath and cord, the sheath is retracted to expose a second portion of the cord. The second portion of the cord is then moved into a desired position relative to another anchor member such that the spacer is positioned between the two anchor members.

FIELD OF THE INVENTION

This invention relates to surgical methods and associated installationsystems for spinal stabilization, and more particularly to such systemsand methods of inserting a flexible spinal stabilization element into apatient.

BACKGROUND

The spinal column is a highly complex system of bones and connectivetissues that provides support for the body and protects the delicatespinal flexible connecting member and nerves. The spinal column includesa series of vertebrae stacked one on top of the other, each vertebralbody including an inner or central portion of relatively weak cancellousbone and an outer portion of relatively strong cortical bone. Situatedbetween each vertebral body is an intervertebral disc that cushions anddampens compressive forces experienced by the spinal column. A vertebralcanal containing the spinal cord and nerves is located posterior to thevertebral bodies. In spite of the complexities, the spine is a highlyflexible structure, capable of a high degree of curvature and twist innearly every direction. For example, the kinematics of the spinenormally includes flexion, extension, rotation and lateral bending.

There are many types of spinal column disorders including scoliosis(abnormal lateral curvature of the spine), kyphosis (abnormal forwardcurvature of the spine, usually in the thoracic spine), excess lordosis(abnormal backward curvature of the spine, usually in the lumbar spine),spondylolisthesis (forward displacement of one vertebra over another,usually in a lumbar or cervical spine) and other disorders caused byabnormalities, disease, or trauma, such as ruptured or slipped discs,degenerative disc disease, fractured vertebra, and the like. Patientsthat suffer from such conditions usually experience extreme anddebilitating pain as well as diminished range of motion and nervefunction. These spinal disorders may also threaten the critical elementsof the nervous system housed within the spinal column.

One of the most common methods for treating spinal disorders is toimmobilize a portion of the spine to allow treatment. Traditionally,immobilization has been accomplished by rigid stabilization. Forexample, in a conventional spinal fusion procedure, a rigid fixation rodis installed between pedicle screws secured to adjacent vertebrae. Thefixation rod cooperates with the screws to immobilize the two vertebraerelative to each other so that fusion may occur. Fusion treatments usingrigid stabilization, however, do have some disadvantages. For example,because the immobilized portion of the spine has reduced mobility,additional stresses are transferred to other portions of the spineneighboring or nearby the fused vertebrae. Fusion is also anirreversible procedure.

More recently, dynamic stabilization has been used in spinal treatmentprocedures. Dynamic stabilization does not result in complete spinalfusion, but instead permits enhanced mobility of the spine while alsoproviding sufficient stabilization to effect treatment. One example of adynamic stabilization system is the Dynesys® system available fromZimmer Spine, Inc. of Edina, Minn. Such dynamic stabilization systemstypically include a flexible spacer positioned between pedicle screwsinstalled in adjacent vertebrae of the spine. Once the spacer ispositioned between the pedicle screws, a flexible cord is threadedthrough a channel in the spacer. The flexible cord is also secured tothe pedicle screws by a retainer and set screw, thereby retaining thespacer between the pedicle screws while cooperating with the spacer topermit mobility of the spine.

The dynamic stabilization systems described above and others arenaturally installed in a patient during a surgical procedure. Patientrecovery from such surgical procedures is greatly enhanced if thetissue, muscle and other parts of the patient that are displaced andaffected by the surgery are minimized, including the size and severityof the required incisions. For example, the cord can be inserted througha “puncture hole” or “access channel” used to implant one of the pediclescrews and then advanced to its installed position between the pediclescrews. Due to its flexible nature, however, the cord can be difficultto maneuver through the tissue. Additional tools are often required toaccomplish this positioning. As a result, the access channels for thepedicle screws must be made large enough to accommodate the tools andany manipulation required. Increasing the size of the access channelsincreases the disruption of muscle tissue, which should be minimized toreduce scarring and promote faster recovery times. Therefore, systemsand methods that further reduce the amount of disruption to the muscletissue are highly desirable.

SUMMARY OF THE INVENTION

This invention provides a system and method of inserting a flexiblespinal stabilization element into a patient. The flexible spinalstabilization system generally includes an elongated flexible element,such as a cord, configured to be secured to first and second anchormembers, such as pedicle screws, within the patient's body. The systemalso includes a spacer configured to be received over the flexibleelement. Those skilled in the art will appreciate, however, that othersystems having similar components may be inserted into a patientaccording to the invention as well.

To insert the system, the flexible element is positioned within asheath. The sheath may be formed from any suitable material forinsertion into a patient's body. Advantageously, the sheath may beformed from a material having greater rigidity than the flexibleelement. The sheath and the flexible element are inserted into thepatient's body at a first location on the patient's skin and along apath generally toward one of the anchor members. For example, the sheathand the flexible element may be inserted through the patient's skin at alocation generally above the first anchor member and directed throughthe patient's body along a path extending toward the second anchormember. The shape of the sheath may help define the path, which mayinclude a combination and straight and curved portions. The inventionmay also include a rigid advancement member mounted on the leading endof the flexible element for easier insertion, protection of the implantcomponents, and other benefits described herein.

Once inserted or during the insertion, the sheath is retracted to exposea first portion of the flexible element within the patient's body. Thefirst portion of the flexible element is then positioned in a desiredposition relative to the second anchor member. For example, the anchormember may be a pedicle screw having a retainer or head portion with aslot configured to receive the flexible element. In such an embodiment,the first portion of the flexible element may be positioned until it isproperly located in the corresponding portion of the anchor member. Aset screw or the like may be used to secure the first portion to theanchor member.

The system and method of inserting the stabilization system furthercomprises advancing a spacer over the sheath and the flexible element.After retracting the sheath to expose a second portion of the flexibleelement within the patient's body, the second portion of the flexibleelement is positioned relative to the first anchor member so that thespacer is positioned between the first and second anchor members. Thesecond portion of the flexible element may be secured to the firstanchor member similar to the way the first portion is secured to thesecond anchor member or in a different manner. Additionally, theflexible element may be cut proximate the second portion to define aseparate segment.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of theinvention and, together with a general description of the inventiongiven above, and the detailed description given below, serve to explainthe principles of the invention.

FIG. 1 is a schematic view showing a portion of a flexible spinalstabilization system being inserted into a patient according to variousembodiments of this invention;

FIG. 1A is a perspective view of the portion of the flexible spinalstabilization system illustrated in FIG. 1; and

FIGS. 2-5 are schematic views sequentially illustrating the flexiblespinal stabilization system of FIG. 1 being further inserted into thepatient.

DETAILED DESCRIPTION

FIGS. 1-5 illustrate an exemplary embodiment of a dynamic spinalstabilization system 10 being inserted into the body 12 of a patient.The stabilization system 10 generally includes first and second anchormembers 20, 22 secured to first and second vertebrae 24, 26 in thepatient's body 12, a cord 30 configured to extend between the first andsecond anchor members 20, 22, and a spacer 32 configured to be receivedover the cord 30 between the first and second anchor members 24, 26. Thecord may be formed, for example and without limitation, frompolyethylene terephthalate (PET), titanium or metal materials, or othersuitable materials recognized by those of skill in the art. The spacer32 may be formed, for example and without limitation, frompolycarbonate-urethane (PCU), polymeric and/or flexible materials, orother suitable materials recognized by those of skill in the art. In oneembodiment, the stabilization system 10 is the Dynesys® system availablefrom Zimmer Spine, Inc. of Edina, Minn. Those skilled in the art willappreciate, however, that the invention described below applies equallyto other stabilization systems having similar components and/oroperating upon similar principles.

Prior to inserting the stabilization system, the first and second anchormembers 20, 22 are inserted into the patient's body 12. The first andsecond anchor members 20, 22 may be inserted using any technique knownin the art. In one embodiment, a first incision 40 is made at a firstlocation on the patient's skin 42 generally aligned above the firstvertebra 24. The first anchor member 20 is inserted through the firstincision 40 and advanced through the patient's body 12 so that it may besecured to the first vertebra 24. If desired, an access channel orpuncture hole 44 may be established from the first incision 40 to thefirst vertebra 24 before inserting the first anchor member 20. Theaccess channel 44 may be created by a needle or dilator (not shown) andoptionally maintained by a cannula, retractor, or the like (not shown).Alternatively, the first anchor member 20 is driven through the body 12after making the incision 40 to thereafter establish the access channel44.

The second anchor member 22 may be inserted into the body 12 in a mannersimilar as the first anchor member 20. Specifically, a second incision50 may be made at a second location on the patient's skin 42 generallyaligned above the second vertebra 26. A second access channel 52 isestablished at the second incision 50, and the second anchor member 22is advanced into the patient's body 12 so that it may be secured to thesecond vertebra 26. A wide variety of anchor members may be used withthe stabilization system 10. The first and second anchor members 20, 22shown in the drawings each include a pedicle screw 54 having a retainermember or housing 60 coupled to a top portion of the screw 54. As shownin FIG. 1A, each housing 60 includes a slot 62 configured to receive aportion of the cord 30. The housing 60 also includes internal threads 64for receiving a set screw 66 (FIGS. 2-5), as will be described ingreater detail below.

Prior to insertion, the cord 30 is positioned within a protective sheath70. The sheath 70 may be made from any type of material suitable forinsertion into a patient's body. In one embodiment, the sheath 70 isconstructed from flexible polyethylene tubing having a rigidity greaterthan that of the cord 30. The strength of the sheath 70 and its abilityto withstand compression forces enables it to be advanced through thetissue in the patient's body 12 without being significantly deflected.In other embodiments, the sheath can be constructed of materials such asmetal to provide greater rigidity. Additionally, the cord 30 can beconstructed from a flexible shape memory material such as nitinol. Inits preferred configuration, the shape memory cord 30 can have astraight configuration. After loading the cord 30 into the sheath 70 orsurrounding it with the sheath 70, the shape memory cord 30 can take onor conform to the configuration of the sheath 70. For example, the shapememory cord 30 can go from straight to curved. After receiving thesheath 70, the shape memory cord 30 can return to its preferred straightconfiguration within the housing 60 of an anchor member 20, 22.

Additionally, an advancement member 84 may be mounted on a leading end34 of the cord 30 and in advance of the sheath 70. The advancementmember 84 may be metal or any other type of material suitable forinsertion into the patient's body 12. The advancement member 84 mayinclude a leading tip 85 to facilitate movement of the cord 30 and/orsheath 70 through tissue, a main body portion 88, and a receiver section86 adapted to accept the leading end 34 of the cord 30 and/or theleading end of the protective sheath 70. Furthermore, the advancementmember 84 may have any configuration, including a bent or curvedprofile, to assist the surgeon when inserting the advancement member 84,cord 30, and sheath 70 into the patient. The advancement member 84offers the advantages of easier insertion of the cord 30 into thepatient, may provide fluoroscopy marking, and protects the cord 30 orother implant during manipulation by the surgeon with clamps or otherinstruments. The tip 85 can have any configuration such as a needle,bullet nose, or tapered shape to facilitate movement through tissue.

Therefore, as shown in FIG. 1, the advancement member 84, sheath 70, andcord 30 are inserted through the first incision 40 and along a path 72through the patient's body 12 generally toward the second anchor member22. The cord 30 may be positioned within the sheath 70 and advancementmember 84 such that no portion of the cord 30 is directly exposed to thepatient's body 12 during this insertion. Alternatively, the end 34 ofthe cord 30 may extend slightly beyond the sheath 70, but not far enoughto significantly affect the insertion of the sheath 70 and the cord 30.The path 72 along which the advancement member 84, cord 30, and sheath70 are inserted may include a combination of generally straight sectionsand curved sections. For example, in one embodiment, the path 72includes a first generally straight section 74, an intermediate curvedsection 76, and a second generally straight section 78. Such anarrangement allows the sheath 70 and the cord 30 to be “fished”downwardly for a distance before being directed transversely toward thesecond anchor member 22.

At some point after or during the insertion, the advancement member 84is removed through the incision 50 and the sheath 70 is retracted toexpose a first portion 80 of the cord 30 within the patient's body 12.Alternatively, the cord 30 can be affixed to the advancement member 84and the cord 30 is pulled up through the incision 50. The excess portionof the cord 30 can then be cut off the flexible construct.

The first portion 80 of the cord 80 is proximate the end 34. As shown inFIG. 2, the first portion 80 is moved into a desired position relativeto the second anchor member 22. This may involve positioning the firstportion 80 of the cord 30 in the slot 62 of the associated housing 60. Apositioning tool 82 may be inserted through the second access channel 52to push the first portion 80 of the cord 30 into the slot 62. Thepositioning tool 82 may be the same or a different tool than that usedto deliver a set screw 66 to the second anchor member 22.

FIG. 3 illustrates the system lo after the first portion 80 of the cord30 is secured to the second anchor member 22. Specifically, the setscrew 66 has been inserted through the second access channel 52 and intothe housing 60 of the second anchor member 22. External threads (notshown) on the set screw 66 engage the internal threads 64 (FIG. 1A) ofthe housing 60 to secure the components. The set screw 66 cooperateswith the housing 60 to secure the first portion 80 so that the cord 30cannot be easily pulled away from the second anchor member 22. Althoughonly the set screw 66 is shown, a wide variety of other devices orfastening elements may be used to secure the first portion 80 instead ofor in addition to the set screw 66. For example, the second anchormember 22 may alternatively include a portion adapted to cooperate witha cap (not shown) for retaining the first portion 80 of the cord 30.

Still referring to FIG. 3, the spacer 32 is advanced over the sheath 70and the cord 30 into the patient's body 12. Alternatively, the sheath 70can be removed and the spacer 32 placed directly over the cord 30. Thespacer 32 is advanced until a first end 36 is positioned proximate thesecond anchor member 22. For example, the spacer 32 may be advanceduntil the first end 36 abuts the retainer element 60 of the secondanchor member 22. As shown in FIG. 4, the sheath 70 is further retractedto expose a second portion 90 of the cord 70, which is moved into adesired positioned relative to the first anchor member 20 so that thespacer 32 extends between the first and second anchor members 20, 22.The sheath 70 may be retracted before or during the positioning of thesecond portion 90. Additionally, as with the first portion 80, apositioning tool 92 maybe inserted through the first access channel 44to push the second portion 90 into the slot 62 of the housing 60. A setscrew 94 or other device is used to secure the second portion 90 withinthe housing 60.

FIG. 5 illustrates a cord segment 96 formed after cutting the cord 30proximate the second portion 90. The cord segment 96 includes the firstand second portions 80, 90 and extends between the first and secondanchor members 20, 22. The remainder of the cord 30 (not shown) fromwhich the segment 96 was cut has been removed from the patient's body 12through the first incision 40.

As a result of the above-described insertion procedure, the need tocreate incisions or access channels large enough to accommodate toolsfor maneuvering the cord 30 through tissue is reduced or eliminated. Theadvancement member 84 and/or protective sheath 70 are able to guide thecord through tissue along a desired path. To this end, the inventiontakes advantage of the incisions already made to insert the first andsecond anchor members 20, 22, thereby reducing or minimizing anyadditional disruption of tissue required to complete the surgicalprocedure. If desired, however, the cord 30 may be inserted through anincision or access channel different than those used to implant thefirst and second anchor members 20, 22. Use of the advancement member 84and/or protective sheath 70 also allow for aseptic handling of the cord30 prior to its final placement within the patient's body 12. Suchhandling helps reduce the risk of deep wound infections.

While the invention has been illustrated by the description of one ormore embodiments thereof, and while the embodiments have been describedin considerable detail, they are not intended to restrict or in any waylimit the scope of the appended claims to such detail. Additionaladvantages and modifications will readily appear to those skilled in theart. For example, the invention described above may be used to positionthe cord 30 between more than two anchor members or more than twovertebrae. To this end, the cord 30 may be positioned between first,second, and third anchor members secured to respective first, second,and third vertebrae. Additionally, the sheath 70 and cord 30 may beinserted into the patient's body 12 with the first portion 80 alreadypartially or fully exposed. Moreover, the sheath is shown and describedin one embodiment as being a tubular member, but the sheath may be ofanother configuration that may or may not entirely surround the cord, ahelical element or some other structure extending over a length of thecord and providing added rigidity to the cord during installation. Thesheath may include multiple component parts assembled together from thesame or variety of different materials.

The invention in its broader aspects is therefore not limited to thespecific details, representative apparatus and methods and illustrativeexamples shown and described. Accordingly, departures may be made fromsuch details without departing from the scope or spirit of theinventor's general inventive concept.

1. A method of inserting a spinal stabilization system into a patient,the spinal stabilization system including a flexible element configuredto be secured to first and second anchor members within the patient'sbody, each of the first and second anchor members having a housingincluding an open slot defined between opposing legs of the housing, themethod comprising: coupling the flexible element with a sheath;inserting the sheath and the flexible element through a first locationon the patient's skin and along a path through the patient's bodygenerally toward the second anchor member simultaneously; retracting thesheath to expose a first portion of the flexible element within thepatient's body; positioning the exposed first portion of the flexibleelement in the slot of the second anchor member; advancing a spacer overthe flexible element such that the spacer is positioned between thefirst and second anchor members after the first portion of the flexibleelement is positioned in the slot of the second anchor member;retracting the sheath to expose a second portion of the flexible elementwithin the patient's body; and after advancing the spacer over theflexible element to a position between the first and second anchormembers, positioning the exposed second portion of the flexible elementin the slot of the first anchor member.
 2. The method of claim 1 whereinthe flexible element is within the sheath during advancement of thespacer over the flexible element.
 3. The method of claim 1, furthercomprising: cutting the flexible element proximate the second portion.4. The method of claim 1 wherein the inserting the sheath and theflexible element through the first incision and along the path stepfurther comprises: directing the sheath and the flexible elementdownwardly along a first generally straight section of the path, througha curved section of the path, and toward the second anchor member alonga second generally straight section of the path.
 5. The method of claim1 wherein the sheath and the flexible element are inserted through afirst incision at the first location on the patient's skin, and whereinthe positioning the exposed first portion of the flexible element stepfurther comprises: inserting a positioning tool through a secondincision at a second location on the patient's skin and through thepatient's body to push the first portion of the flexible element towardthe second anchor member; and receiving the first portion of theflexible element in the slot of the second anchor member.
 6. The methodof claim 5 wherein the positioning the exposed first portion of theflexible element step further comprises: securing the first portion ofthe flexible element to the second anchor member.
 7. The method of claim5 wherein the positioning the exposed second portion of the flexibleelement step further comprises: inserting a positioning tool through thefirst incision and into the patient's body to push the exposed secondportion of the flexible element toward the first anchor member; andreceiving the exposed second portion of the flexible element in the slotof the first anchor member.
 8. The method of claim 7 wherein thepositioning the exposed second portion of the flexible element stepfurther comprises: securing the exposed second portion of the flexibleelement to the first anchor member.
 9. The method of claim 1 wherein theinserting the sheath and the flexible element through the first locationon the patient's skin step further comprises: inserting the sheath andthe flexible element through the patient's skin at a location generallyaligned with the first anchor member.
 10. The method of claim 1, furthercomprising: positioning an advancement member relative to the sheath toprotect the flexible element, and wherein inserting the sheath and theflexible element through the first location on the patient's skinfurther comprises inserting the advancement member through the firstlocation.
 11. The method of claim 10 wherein the positioning theadvancement member relative to the sheath step further comprises:mounting the advancement member to a leading end of the flexibleelement.
 12. The method of claim 10 wherein the positioning theadvancement member relative to the sheath step further comprises:mounting the advancement member to a leading end of the sheath.
 13. Themethod of claim 10, further comprising: removing the advancement memberfrom the patient's body through a second location on the patient's skin.14. A method of inserting a spinal stabilization system into a patient,comprising: creating a first and second incisions in the patient's skin;establishing first and second access channels extending from therespective first and second incisions to respective first and secondlocations within the patient's body; inserting first and second anchormembers in the patient's body through the respective first and secondaccess channels; positioning a flexible element within a sheath;inserting the sheath and the flexible element through the first incisionand along a path generally toward the second anchor member; retractingthe sheath to expose a first portion of the flexible element within thepatient's body; securing the exposed first portion of the flexibleelement to the second anchor member; advancing a spacer over the sheathand the flexible element such that the spacer is positioned between thefirst and second anchor members after the first portion of the flexibleelement is secured to the second anchor member; retracting the sheath toexpose a second portion of the flexible element within the patient'sbody; and after the spacer is advanced over the flexible element to aposition between the first and second anchor members, securing theexposed second portion of the flexible element to the first anchormember.
 15. The method of claim 14, wherein the flexible element ispositioned within the sheath prior to inserting the sheath through thefirst incision and along a path generally toward the second anchormember.
 16. The method of claim 14, further comprising: cutting theflexible element proximate the second portion.
 17. The method of claim14 wherein the inserting the sheath and the flexible element through thefirst incision and along the path step further comprises: directing thesheath and the flexible element downwardly along a first generallystraight section of the path, through a curved section of the path, andtoward the second anchor member along a second generally straightsection of the path.
 18. The method of claim 14 wherein the securing theexposed first portion of the flexible element step further comprises:inserting a positioning tool through the second access channel to pushthe exposed first portion of the flexible element toward the secondanchor member; and receiving the exposed first portion of the flexibleelement in an open slot of the second anchor member.
 19. The method ofclaim 18 wherein the securing the exposed second portion of the flexibleelement step further comprises: inserting a positioning tool through thefirst access channel to push the exposed second portion of the flexibleelement toward the first anchor member; and receiving the exposed secondportion of the flexible element in an open slot of the first anchormember.
 20. The method of claim 14, further comprising: positioning anadvancement member relative to the sheath to protect the flexibleelement, and wherein inserting the sheath and the flexible elementthrough the first incision further comprises inserting the advancementmember through the first incision.
 21. The method of claim 20 whereinthe positioning the advancement member relative to the sheath stepfurther comprises: mounting the advancement member to a leading end ofthe flexible element.
 22. The method of claim 20, further comprising:removing the advancement member from the patient's body through thesecond incision.